The episode begins as Amaya happily enters the school to give out her owl invitations to Marie and Jenny for her super fun pajama party. When she gives an invitation to Marie, though, a couple of moths pop out of the envelope and take the invitation with them. Amaya asks Marie to share her invitation with Jenny, and the two girls head to class. At the same time, Connor and Greg meet up with Amaya, and she tells them about the moths inside her backpack. Betting that Luna Girl is planning to ruin her sleepover party, she becomes determined to protect the nighttime event.
That night, the PJ Masks arrive at HQ and look at the PJ Picture Player for any signs of the villainess. There are none so far, but given the previous events, she will be up to mischief at some point. With that in mind, Catboy and Gekko promise to be on the lookout throughout the whole neighborhood while Owlette enjoys her sleepover with her friends.
Owlette flies to her house as Marie and Jenny arrive with their costumes on. She welcomes them, but she notices Luna Girl arriving and tells the girls to go on a treasure hunt around the garden. Owlette confronts Luna Girl as she takes a couple of things from her party, but she pushes her down as Marie finds a present behind one of the bushes. The three girls then proceed to take selfies, but when Owlette looks at the photos, she sees Luna Girl in all of them. She tells the girls to play hide-and-seek in the house, and confronts the villainess one last time before following them in, telling her that her party is for guests only, despite the stolen invitation, and that she is not ruining it.
Angered, Luna Girl decides to have her own sleepover party and takes the party snacks. Catboy and Gekko, after being contacted about her presence, arrive to stop Luna Girl, but she leads them on a chase to catch the food. She then bubbles the boys, and she brings them to the park to hold her sleepover. There, she takes a selfie with the two annoyed heroes and leaves them there to collect the party games next.
Meanwhile, Owlette finds Marie and Jenny in her room. She opens up her laptop to play a movie, and the two girls watch while Owlette looks outside her window for Catboy and Gekko. She flies outside, and she meets Luna Girl again. She demands her to tell her where Catboy and Gekko are, to which she responds that they are playing hide-and-seek at her own party, and she must find them on her own. Annoyed, Owlette starts looking around, while Luna Girl flies off to find some more guests for her party.
Luna Girl looks inside Owlette’s room and sees Marie and Jenny sleeping as the movie ends. Feeling that the girls will have a much better time at her party, she bubbles the girls and prepares to take them away to the park, only for Owlette to blow her away. The girls are safe, but she doesn’t know how to free them. Luna Girl is blown to the park when Motsuki arrives, mocking her. Luna Girl tells her about her sleepover, but she is not invited to it since she might ruin it. Motsuki leaves, and Owlette approaches Luna Girl, telling her to free her friends.
The two girls return to Owlette’s house when they see Motsuki there. Wanting to have her own sleepover party, she prepares to take Marie and Jenny to the moon. In response, Owlette uses her Super Owl Feathers to push Motsuki away. She pushes her friends inside her room and barricades the window. She and Luna Girl then go inside, and the villainess compliments her on her room. She prepares to un-bubble Marie and Jenny, but the girls hear Motsuki’s moth sounds.
They fly out to the park, and they see Motsuki bubbling Owlette’s party supplies and Catboy and Gekko so she can take all of them to the moon. Owlette blows her away before she could teleport the bubbles, but this does not faze her as the bubbles can float up there anyway. She disappears to wait, leaving Owlette indecisive about which bubbles are her teammates, but Luna Girl volunteers to help her, though, since she is responsible for this mess. Owlette accepts, and Luna Girl pops the bubbles while she catches anything that falls out. Soon enough, all the bubble shields are popped, and everything and Catboy and Gekko are saved.
Owlette compliments Luna Girl on a job well done, saying that they work pretty well together when she is not so bad. Luna Girl suddenly realizes that this must be the reason why she was not invited to her sleepover. Owlette feels bad about hurting her feelings, and decides to make this right by writing her a legitimate invitation to the event, with the promise of behaving for tonight, to which Luna Girl happily accepts. Motsuki suddenly arrives and complains about her party being ruined. Luna Girl offers her a chance to join the group if she asks nicely, but Motsuki refuses and leaves.
Everyone returns to Owlette’s room, and Luna Girl un-bubbles Marie and Jenny. The girls wake up, and they compliment on everyone's costumes, especially Luna Girl’s. She thanks them and thanks Owlette for inviting her to her slumber party. The party begins, and everyone gathers in for a group selfie, with Owlette taking into heart Luna Girl’s funny face.
You shouldn't exclude others in an event or party.
It is revealed that Cameron's sister's name is Marie, while the blond girl with the glasses' name is Jenny.
And while the former occasionally appeared with Cameron in most episodes beginning with "Catboy's Cuddly", the latter was more or less a background character.
This is the third episode where the PJ Masks don't say their signature victory chant "PJ Masks, all shout 'hooray'! 'Cause in the night we saved the day!" in the end.